There are several possible ways, depending on whether the array is ordered and whether you wish to preserve the ordering.

a) If @in is sorted, and you want @out to be sorted: (this assumes all true values in the array)

Code

$prev = 'nonesuch'; @out = grep($_ ne $prev && ($prev = $_), @in);

This is nice in that it doesn't use much extra memory, simulating uniq(1)'s behavior of removing only adjacent duplicates. It's less nice in that it won't work with false values like undef, 0, or ``''; ``0 but true'' is ok, though.